While on the subject of physical computing, you can’t get much more physical than the pulse from a human body. pixelcrypt has created a piece that synthesizes music using human pulse. Two participants can collaborate on the music by regulating their pulse; the sonic feedback means this interactive art piece also doubles as an excellent example of biofeedback. Working together, you can synchronize your pulses. (I dream of the day when I can receive MIDI Time Code, but until then . . .)
The whole thing is built in Max/MSP: plug in a sensor, and play. And yes, this is yet another example of why Max is a compelling tool for translating data from sensors into sound and imagery. It’s music with heart.